EX-773 lnet: RMDA infrastructure updates

EX-773 lnet: RMDA infrastructure updates

Add infrastructure to force RDMA for payloads < 4K.
Add infrastructure to extract the first page in a
payload. Useful for determining the type of the payload
to be transmitted.

Signed-off-by: Amir Shehata <ashehata@whamcloud.com>
Change-Id: Id7dc26c83f00dadd26feca94fc4d8233872650d3
Reviewed-on: https://review.whamcloud.com/37453
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/42000
Reviewed-by: Wang Shilong <wshilong@whamcloud.com>